In a previous study (Z01.00001) with a sample composed largely of infants and mothers of low socioeconomic status, significant relationships were found between specific early environmental variables and specific aspects of infant development at 6 months. For example, the mother's contingent response to the infant's cry was significantly related to both the Mental and Psychomotor Developmental Indexes on the Bayley Test. Kinesthetic stimulation by the mother was also related to measures of Goal Directedness, Object Permanence and Social Responsiveness. Because of the theoretical significance of these findings, we are replicating the previous study with a middle-class sample. The sample consists of 49 infants, 25 boys and 24 girls and their mothers, of middle socioeconomic status. Data on environmental variables are being obtained through time-sampling observations in the home with the mother-infant interaction schedule developed in the previous study. Measures of infant characteristics are obtained from the Bayley Scales of Infant Development and through a structured test designed to measure exploratory behavior and preference for novel stimuli.